Prompted by societal concerns and demands concerning the disposal of plastic products such as plastic films, research is being done on biodegradable resin compositions. Active efforts are underway to develop biodegradable aromatic polyester resin compositions which are degradable under the high-humidity, high-temperature conditions associated with waste composting processes. Various uses are being proposed for such compositions. For example, Tokuhyo Hei 5-7507109, 6-505513 and 6-505040 describe polyesters prepared by polymerizing a glycol component made of ethylene glycol and diethylene glycol with two acid components; namely, an alkali metal or alkaline earth metal salt of a sulfonic acid, and terephthalic acid. These prior-art references also describe fibers, films, sheets and fiber nonwoven fabrics composed of such polyesters.
Tokukai 2001-172487 describes biodegradable moldings with inorganic fillers that are vacuum molded from aliphatic polyester sheet. Such moldings have improved modulus, thermal resistance and impact resistance.
Tokukai Hei 9-169897 describes biodegradable sheet with natural fibers. Such sheet has enough strength and heat resistance during use.
Such thermoplastic materials including polyolefin, polyester, polyamide and polyvinyl chloride are useful in molding articles by any of the techniques commonly used with thermoplastic materials, e.g., compression molding, injection molding, extrusion, and blow molding. However, in certain applications such as daily necessities, electronics, appliances, industrial applications and automobile applications, products made from biodegradable polymer would be desirable. Also desirably, the biodegradable polymer would have mechanical strength and heat resistance not less than those of products made from such other thermoplastic materials. It is also well known that addition of fillers into aliphatic polyester molding compositions may improve heat resistance and modulus of elasticity, but may not improve molding cycle, mold release and moldability enough to meet the requirements of the above applications. As noted above, aliphatic polyester resins have improved strength and heat resistance by adding fillers. Yet, they continue to lack sufficient stiffness, impact resistance and heat resistance for practical use in applications such as daily necessities, electronics, appliances, industrial applications and automobile applications. Moreover, when aliphatic polyesters with fillers are injection molded, this causes low moldability such as low mold releasability or long molding cycle.